Preheat oven to 350°F (175°C). Prepare the tart crust by mixing flour, cocoa powder, powdered sugar, and salt.

Cut in cold butter until mixture resembles coarse crumbs.

Add egg yolk and cold water, mix until dough forms. Chill 30–45 minutes.

Roll dough and press into a 9-inch tart pan. Trim edges.

Line crust with parchment and fill with pie weights. Bake 15 minutes. Remove weights and bake 5–7 more minutes. Cool completely.

Prepare ganache: heat cream until simmering, pour over chopped chocolate, let sit 1–2 minutes, stir until smooth. Add butter and vanilla. Pour into cooled crust. Chill 1–2 hours.

Prepare caramel: melt sugar over medium heat until amber. Add butter carefully, then cream slowly while stirring. Stir in sea salt.

Pour caramel over set ganache, swirl gently with a knife.

Chill tart 1 hour until caramel is slightly firm. Serve chilled or at room temperature.